/***
 * 带有尾结点的链表队列:队首出栈,队尾入栈
 */
public class LinkedListQueue<E> implements Queue<E> {

    private class Node {
        public E e;
        public Node next;

        public Node(E e, Node next) {
            this.e = e;
            this.next = next;
        }

        public Node(E e) {
            this(e, null);
        }

        public Node(Node next) {
            this(null, next);
        }

        public Node() {
            this(null, null);
        }

        @Override
        public String toString() {
            return e.toString();
        }
    }

    private Node head, tail;
    private int size;

    public LinkedListQueue() {
        head = null;
        tail = null;
        size = 0;
    }


    @Override
    public E dequeue() {
        if (isEmpty()) {
            throw new IllegalArgumentException("cannot dequeue from an empty queue");
        }
        Node retNode = head;
        head = head.next;
        retNode.next = null;
        if(null == head){
            tail = null;
        }
        size --;
        return retNode.e;
    }

    @Override
    public void enqueue(E e) {
        if (tail == null) {
            tail = new Node(e);
            head = tail;
        } else {
            tail.next = new Node(e);
            tail = tail.next;
        }
        size++;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    @Override
    public E getFront() {
        return head.e;
    }

    @Override
    public String toString() {
        StringBuffer sb = new StringBuffer();
        sb.append("LinkedListQueue front");
        Node cur = head;
        while(cur != null){
            sb.append(cur).append("->");
            cur = cur.next;
        }
        sb.append(" null tail");
        return sb.toString();
    }

    public static void main(String[] args) {
        LinkedListQueue<Integer> linkedListQueue = new LinkedListQueue<>();
        for(int i=0;i<10;i++){
            linkedListQueue.enqueue(i);
            System.out.println(linkedListQueue);

            if(i%3 == 2){
                linkedListQueue.dequeue();
                System.out.println(linkedListQueue);
            }
        }
    }
}
